Removal of volatile organic compound (VOC) from air using zeolite based adsorption-catalytic combustion system
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Date
2007
Authors
Wong, Cheng Teng
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Abstract
The development of an advanced VOC destruction process consists of an adsorption
unit followed by a catalytic combustion system has been proposed in the current study.
The two hydrophobic zeolites, namely HY (SiO2/Al2O3=80) and ZSM-5 (SiO2/Al2O3=240)
were chosen as adsorbents. Silver metal was loaded on these adsorbents to use as a
catalyst for VOC combustion. The silver-loaded zeolites were tested using butyl acetate
(BA) as a model VOC compound for the adsorption and catalytic combustion system.
The ion exchange (IE) and incipient wetness impregnation (IM) methods were
used to prepare silver-loaded zeolites. The silver-loaded zeolites by impregnation
method did not perform well in the adsorption process. The results showed poor VOC
uptake capacity and early breakthrough time. AgY(IE) showed the highest VOC uptake
capacity and the adsorbent service time was much longer compared to AgZSM-5(IE).
The presence of water vapour in the feed suppressed the VOC adsorption capacity of
AgY(IE) due to the competitive adsorption of water vapour on the active sites. However,
VOC adsorption capacity of AgZSM-5(IE) was not affected in the presence of water
vapour. A central composite design (CCD) was used to study the effect of three
important operating parameters (VOC concentration, relative humidity, GHSV) for
adsorption process. The response surface methodology (RSM) was used to obtain the
optimum operating conditions for the adsorption process.
AgY(IE) and AgZSM-5(IE) were tested for VOC uptake data at different
temperatures. A mathematical model was used to evaluate the thermodynamic
behaviour in conjunction with the Langmuir isotherm for the adsorption of butyl acetate
over AgY(IE) and AgZSM-5(IE). The model parameters were evaluated and used to
predict the adsorption isotherms and breakthrough curves under various process
conditions.
The performance of silver loaded zeolite catalysts in combustion of VOC was
studied with the objective of developing a catalyst with superior activity, selectivity
towards deep oxidation product and stability. The catalyst activity was measured in the
reactor operated at GHSV = 15,000 h-1, reaction temperature between 150oC - 500oC
and VOC inlet concentration of 1000ppm. AgY(IE) and AgZSM-5(IE) exhibited high
activity in the combustion of butyl acetate where total conversion of butyl acetate was
achieved at temperature below 400oC. A central composite design was used to study
the effect of three important operating parameters (VOC concentration, reaction
temperature, GHSV) for combustion process. The response surface methodology was
used to obtain the optimum operating conditions for the combustion process.
The combustion data of butyl acetate were fitted to a simple model following
power-law rate equation. The reaction orders, n and m were evaluated by varying the
VOC partial pressure between 0.004 to 0.018 atm and partial pressure of oxygen
between 0.05 to 0.20 atm. The activation energies were 26.30 kJ/mol and 20.65 kJ/mol
for AgY(IE) and AgZSM-5(IE), respectively.
Description
Master
Keywords
Chemical Engineering , Volatile organic compound , Zeolite , Adsorption-catalytic combustion system